Air Flow

[prprog]

How can I make this opamp amp. detect air flow? What I need is that the Electret mic. (EM) detect air flow and make the LED change light intensity based on how strong the air flow is. (I probably put the LED direction wrong in the diagram - sorry). Right now the LED intensity is very - very small . If I need to change the gain of the opamp , how do I do that?

Note: Those are the components I have on hand, the LM324 and the electrec mike.

Thanks,

 

[Externet]

That circuit, if works, would be a noise indicating led. Not windspeed measuring.

A way to do it is with two thermistors, one exposed to the air flow and the other not.

The difference in readings by a differential amplifier will be proportional to the wind speed.

Miguel

 

[prprog]

That circuit, if works, would be a noise indicating led. Not windspeed measuring.

A way to do it is with two thermistors, one exposed to the air flow and the other not.

The difference in readings by a differential amplifier will be proportional to the wind speed.

Miguel

What changes are needed to the circuit to make it work for air flow measurement.?

...on the other hand I want to measure human breath air flow, can the thermistor pair is usable for that purpose? Can you provide a circuit?

Thanks,

 

[Willbe]

https://www.google.com/search?hl=en&q="King's+law"+flow

 

[Boncuk]

Hi prprog,

to measure human breath use low voltage low current lamps. Break the glasses leaving the filaments untouched.

Build two of the filaments into an enclosure with a mouth piece in front.

One of the filaments must be shielded from air movement by making an extra enclosure inside the overall enclosure with small holes so the filament will gain breath temperature - but no cooling because of air movement.

Ideally both filaments should have the same resistance at equal temperature. Compensate for differences using a shunt.

This is the "sensor" arrangement. (Attachment)

Boncuk

 

[Externet]

For atmospheric air flow, search anemometers. I saw very sensitive ones, handheld and low cost perhaps at a kite store on the web, cannot remember.
For medical applications, where a life may depend on reliability of the device, building an unproved project may not be a good idea.

For minute changes in air flow, I would consider piezoelectric film. It looks like cellophane with terminals, and produces a considerable signal when bends forth and back, easily driving a operational amplifier.
To obtain quantitative measurements, some calculations should be added to the measurements; as deflection and duration.
For qualitative detection, it would be much simple.

I have a couple and did not think of an application, until now with your question.

https://www.imagesco.com/catalog/sensors/film.html#pz-01

Perhaps will work fine for you. At least is an alternative to consider
Miguel

 

[Mikebits]

That circuit, if works, would be a noise indicating led. Not windspeed measuring.

A way to do it is with two thermistors, one exposed to the air flow and the other not.

The difference in readings by a differential amplifier will be proportional to the wind speed.

Miguel

Not a bad idea. Not bad at all

 

[KMoffett]

To expand on Boncuk's and Miguel's suggestion...feed the differential amp with a Wheatstone bridge made of 4 lamp filaments. Two in the air flow path and two in still, ambient air. Gives you twice the output, and compensates for changes in ambient air temp.

The lamps in my circuit are just ones I happen to have in the junk box, and the voltage is what seemed to work with these lamps.

Ken